The wall of a ma­jor dam in south­ern Ukraine col­lapsed Tues­day, trig­ger­ing floods, en­dan­ger­ing Eu­rope’s largest nu­clear pow­er plant and threat­en­ing drink­ing wa­ter sup­plies as both sides in the war scram­bled to evac­u­ate res­i­dents and blamed each oth­er for the de­struc­tion.

Ukraine ac­cused Russ­ian forces of blow­ing up the Kakhov­ka dam and hy­dro­elec­tric pow­er sta­tion on the Dnieper Riv­er in an area that Moscow con­trols, while Russ­ian of­fi­cials blamed Ukrain­ian bom­bard­ment in the con­test­ed area. It was not pos­si­ble to ver­i­fy the claims.

The po­ten­tial­ly far-reach­ing en­vi­ron­men­tal and so­cial con­se­quences of the dis­as­ter quick­ly be­came clear as homes, streets and busi­ness­es flood­ed down­stream and emer­gency crews be­gan evac­u­a­tions; of­fi­cials raced to check cool­ing sys­tems at the Za­por­izhzhia Nu­clear Pow­er Plant; and au­thor­i­ties ex­pressed con­cern about sup­plies of drink­ing wa­ter to the south in Crimea, which Rus­sia il­le­gal­ly an­nexed in 2014.

Both Russ­ian and Ukrain­ian au­thor­i­ties brought in trains and bus­es for res­i­dents. About 22,000 peo­ple live in ar­eas at risk of flood­ing in Russ­ian-con­trolled ar­eas, while 16,000 live in the most crit­i­cal zone in Ukrain­ian-held ter­ri­to­ry, ac­cord­ing to of­fi­cial tal­lies. Nei­ther side re­port­ed any deaths or in­juries.

The dam break added a stun­ning new di­men­sion to Rus­sia’s war in Ukraine, now in its 16th month. Ukrain­ian forces were wide­ly seen to be mov­ing for­ward with a long-an­tic­i­pat­ed coun­terof­fen­sive in patch­es along more than 1,000 kilo­me­tres (621 miles) of front line in the east and south.

It was not im­me­di­ate­ly clear whether ei­ther side ben­e­fits from the dam­age to the dam, since both Russ­ian-con­trolled and Ukrain­ian-held lands are at risk. The dam­age could al­so hin­der Ukraine’s coun­terof­fen­sive in the south and dis­tract its gov­ern­ment, while Rus­sia de­pends on the dam to sup­ply wa­ter to Crimea.

Al­though Kyiv of­fi­cials claimed Rus­sia blew up the dam to hin­der the coun­terof­fen­sive, ob­servers note that cross­ing the broad Dnieper would be ex­treme­ly chal­leng­ing for the Ukrain­ian mil­i­tary. Oth­er sec­tors of the front line are more like­ly av­enues of at­tack, an­a­lysts say.

Even so, Nigel Gould-Davies, a se­nior fel­low for Rus­sia and Eura­sia at the In­ter­na­tion­al In­sti­tute for Strate­gic Stud­ies, said the al­leged Russ­ian de­struc­tion of the dam “be­trays a lack of con­fi­dence, a lack of con­fi­dence, a pro­found­ly de­fen­sive mea­sure, the lack of con­fi­dence in Rus­sia’s longer-term prospects” in the war.

Ex­perts have pre­vi­ous­ly said the dam was in dis­re­pair, which could al­so have led to the breach. David Helms, a re­tired Amer­i­can sci­en­tist who has mon­i­tored the reser­voir since the start of the war, said in an email that it wasn’t clear if the dam­age was de­lib­er­ate or sim­ple ne­glect from Russ­ian forces oc­cu­py­ing the fa­cil­i­ty.

But Helms al­so not­ed a Russ­ian his­to­ry of at­tack­ing dams.

Au­thor­i­ties, ex­perts and res­i­dents have ex­pressed con­cern for months about wa­ter flows through — and over — the Kakhov­ka dam. Af­ter heavy rains and snow melt last month, wa­ter lev­els rose be­yond nor­mal lev­els, flood­ing near­by vil­lages. Satel­lite im­ages showed wa­ter wash­ing over dam­aged sluice gates.

Amid of­fi­cial out­rage, Ukrain­ian Pres­i­dent Volodymyr Ze­len­skyy said he con­vened an ur­gent meet­ing of the Na­tion­al Se­cu­ri­ty Coun­cil. He al­leged Russ­ian forces set off a blast in­side the dam struc­ture at 2:50 a.m. (2350 GMT Mon­day) and said about 80 set­tle­ments were in dan­ger. Ze­len­skyy said in Oc­to­ber his gov­ern­ment had in­for­ma­tion that Rus­sia had mined the dam and pow­er plant.

But Krem­lin spokesman Dmit­ry Peskov called it “a de­lib­er­ate act of sab­o­tage by the Ukrain­ian side … aimed at cut­ting wa­ter sup­plies to Crimea.”

Both sides warned of a loom­ing en­vi­ron­men­tal dis­as­ter. Ukraine’s Pres­i­den­tial Of­fice said some 150 met­ric tons of oil es­caped from the dam ma­chin­ery and that an­oth­er 300 met­ric tons could still leak out.

An­driy Yer­mak, the head of Ukraine’s Pres­i­dent’s Of­fice, post­ed a video show­ing swans swim­ming near an ad­min­is­tra­tive build­ing in the flood­ed streets of Russ­ian-oc­cu­pied No­va Kakhov­ka, a city in the Kher­son re­gion where some 45,000 peo­ple lived be­fore the war. Oth­er footage he post­ed showed flood wa­ters reach­ing the sec­ond floor of the build­ing.

Ukraine’s In­te­ri­or Min­istry urged res­i­dents of 10 vil­lages on the Dnieper’s right bank and parts of the city of Kher­son down­riv­er to gath­er es­sen­tial doc­u­ments and pets, turn off ap­pli­ances, and leave, while cau­tion­ing against pos­si­ble dis­in­for­ma­tion.

The Russ­ian-in­stalled may­or of oc­cu­pied No­va Kakhov­ka, Vladimir Leon­tyev, said it was be­ing evac­u­at­ed as wa­ter poured in­to the city.

Ukraine’s nu­clear op­er­a­tor En­er­goatom said via Telegram that the dam­age to the dam “could have neg­a­tive con­se­quences” for the Za­por­izhzhia Nu­clear Pow­er Plant, which is Eu­rope’s biggest, but wrote that for now the sit­u­a­tion is “con­trol­lable.”

The U.N.’s In­ter­na­tion­al Atom­ic En­er­gy Agency said there was “no im­me­di­ate risk to the safe­ty of the plant,” which re­quires wa­ter for its cool­ing sys­tem. It said that IAEA staff on site have been told the dam lev­el is falling by 5 cen­time­ters (2 inch­es) an hour. At that rate, the sup­ply from the reser­voir should last a few days, it said.

The plant al­so has al­ter­na­tive sources of wa­ter, in­clud­ing a large cool­ing pond than can pro­vide wa­ter “for some months,” the state­ment said.

Ukrain­ian au­thor­i­ties have pre­vi­ous­ly warned that the dam’s fail­ure could un­leash 18 mil­lion cu­bic me­ters (4.8 bil­lion gal­lons) of wa­ter and flood Kher­son and dozens of oth­er ar­eas where thou­sands of peo­ple live.

The World Da­ta Cen­ter for Geoin­for­mat­ics and Sus­tain­able De­vel­op­ment, a Ukrain­ian non­govern­men­tal or­ga­ni­za­tion, es­ti­mat­ed that near­ly 100 vil­lages and towns would be flood­ed. It al­so reck­oned that the wa­ter lev­el would start drop­ping on­ly af­ter five-sev­en days.

A to­tal col­lapse in the dam would wash away much of the broad riv­er’s left bank, ac­cord­ing to the Ukraine War En­vi­ron­men­tal Con­se­quences Work­ing Group, an or­ga­ni­za­tion of en­vi­ron­men­tal ac­tivists and ex­perts doc­u­ment­ing the war’s en­vi­ron­men­tal ef­fects.

Mykhai­lo Podolyak, a se­nior ad­vis­er to Pres­i­dent Volodymyr Ze­len­skyy, said that “a glob­al eco­log­i­cal dis­as­ter is play­ing out now, on­line, and thou­sands of an­i­mals and ecosys­tems will be de­stroyed in the next few hours.”

Video post­ed on­line showed flood­wa­ters in­un­dat­ing a long road­way; an­oth­er showed a beaver scur­ry­ing for high ground from ris­ing wa­ters.

The in­ci­dent al­so drew in­ter­na­tion­al con­dem­na­tion, in­clud­ing from Ger­man Chan­cel­lor Olaf Scholz and NA­TO Sec­re­tary-Gen­er­al Jens Stoltenberg, who said the “out­ra­geous act … demon­strates once again the bru­tal­i­ty of Rus­sia’s war in Ukraine.”

Ukraine con­trols five of the six dams along the Dnieper, which runs from its north­ern bor­der with Be­larus down to the Black Sea and is cru­cial for the coun­try’s drink­ing wa­ter and pow­er sup­ply.

Ukraine’s state hy­dro pow­er gen­er­at­ing com­pa­ny wrote in a state­ment that “The sta­tion can­not be re­stored.” Ukrhy­droen­er­go al­so claimed Rus­sia blew up the sta­tion from in­side the en­gine room.

Leon­tyev, the Russ­ian-ap­point­ed may­or, said nu­mer­ous Ukrain­ian strikes on the Kakhov­ka hy­dro­elec­tric plant de­stroyed its valves, and “wa­ter from the Kakhov­ka reser­voir be­gan to un­con­trol­lably flow down­stream.”

Leon­tyev added that dam­age to the sta­tion was be­yond re­pair, and it would have to be re­built.

Ukraine and Rus­sia have pre­vi­ous­ly ac­cused each oth­er of tar­get­ing the dam with at­tacks.

As­so­ci­at­ed Press writer Dan­i­ca Kir­ka in Lon­don con­tributed.

KYIV, Ukraine (AP) —